Protective activity of the F-1 antigen. Preliminary data has suggested that the F-1 capsular antigen induces significant levels of protection. Parts of the proposed research involves expansion of these studies to determine the degree of immunity induced by the F-1 antigen as compared to heat killed cells. Isolation of common antigens. Preliminary results show that serogroups 1, 2, 3, and 4 contain at least 2 common antigens. Studies will be continued to isolate these common antigens and to determine if these antigens will induce significant levels of protection. Conversion of virulent strains of L. pneumophila to avirulent. Preliminary results show that passage of L. pneumophila on laboratory media results in conversion of virulent strains to avirulent. Experiments are planned to document and quantitate this conversion. The role of the macrophage in the hosts defense against infection with L. pneumophila will be studied by examining the phagocytosis of virulent and avirulent strains of L. pneumophila by guinea pig and rat alveolar macrophages. The role of plasmids will be investigated by determining the plasmid composition of virulent and avirulent strains of L. pneumophila.